In the case of blood sugar measurements performed by patients themselves, the patient gives a drop of blood onto the measuring field of a test strip which is then optically measured, with the detector, for example, detecting the color change of the measuring field which is provoked by the application of the blood to the measuring field. The signal produced by the detector corresponds to an average value of the color change in the measuring field. A correct value is thereby obtained only if the amount of blood is sufficient to uniformly wet the entire measuring field. If, in contrast to this, the measuring field is only partially wetted, the measurement becomes falsified since in the making up of the measured value, areas are also included in which practically no chemical reaction results and, therefore, in which no color change takes place. By the time this error is recognized in a customary measurement, a subsequent dosing as a rule is no longer possible because, in the wetted portion of the measuring field, the chemical reaction has already so far advanced that upon further application of blood a uniform coloring of the measuring field is no longer achievable. Moreover, in the case of the patient, as a rule, the small stab wound from which the blood drops have been pressed has again so far closed that no further blood can escape. The patient must, therefore, repeat the measurement, which for him can be very uncomfortable if one remembers that a patient, depending on circumstances, must carry out such measurement several times a day and with each measurement must each time stick himself in the finger.
The invention has as its object the provision of a method of the aforegoing type in which the previously mentioned error can be recognized in time and can be eliminated in the same measurement.